1. Field of the Invention
This invention relates to gas valves for use in vehicles powered by natural gas or other gaseous fuels and to a method of operation thereof. Such valves are connected to high pressure tanks that are utilized to open and close a passageway along which high pressure gaseous fuel flows from the tank to an engine of the vehicle in which the system is installed.
2. Description of the Prior Art
It is known to have gas valves installed on high pressure tanks in motor vehicles. Some previous valves are described in U.S. Pat. Nos. 5,193,580; 5,197,710; and 5,341,844 issued to Wass, et al. Since the solenoid on previous valves must overcome the high tank pressure, previous designs utilize a two-stage process in which a small "bleed" orifice is opened initially, the "bleed" orifice being connected to the downstream gas outlet passageway. With time, the pressure in the outlet passageway gradually builds up so that the pressure differential between the tank and the outlet passageway is greatly reduced. Ultimately, the pressure differential is small enough that the solenoid is able to unseat the main valve, thus allowing the high pressure gas from the tank to have full access to the outlet gas passageway.
Tank pressures are typically in the range of 3600 psi and can rise to much higher values under adverse conditions and a typical diameter for inlet and outlet passageways is around one-third of an inch or larger. It is not unusual therefore to require a force of 300 to 400 pounds to be exerted in order to unseat the valve and, allow gas from the tank full access to the outlet passageway.
Some previous valves are mounted internally and, when the valve malfunctions, it is extremely difficult to make repairs, to vent the tank or to remove the gas pressure from the valve by shutting off the flow of gas from the tank to the valve. Further, if the valve fails, with some previous designs, the motor vehicle cannot be operated. Still further, with previous valves, there is a relatively large time lapse from the turning of the key until the starting of the engine as it can take the valve eighteen seconds or longer to fully open.